1. Field of the invention
The present invention relates to water soluble dyes useful in measuring the glucose levels in an aqueous solution. Also, the present invention is concerned with the synthesis and use of such water soluble dyes.
2. Description of the Prior Art
Measurement of blood glucose levels is very important as basic data for diagnosing and treating diabetics and controlling the meals of diabetic patients. Blood Glucose concentrations have been measured by several methods and they were well known to those skilled in the art.
U.S. Pat. No. 5,605,152 discloses a sensor, composed of optical fibers, which is implanted within a vein of a patient suffering from diabetes, to measure his or her blood glucose levels. The sensor comprises an optode coated with glucose oxidase which oxidizes glucose into gluconic acid and hydrogen peroxide in the presence of oxygen. Blood glucose levels are indirectly detected by measuring the amount of oxygen consumed when the glucose in blood is oxidized. This measuring method, although found to be of somewhat high accuracy, suffers from a disadvantage of being applicable only to the patients who are treated periodically over a long period of time in specialized places, for example, hospitals, because they always carry the sensor within their veins.
Therefore, there remains a need for sensors of measuring blood glucose levels, which are easy to carry with and convenient for the patients slightly suffering from diabetics to use.
A glucose sensor which meets such requirements is found in U.S. Pat. No. 5,779,867. In this patent there is disclosed a self contained glucose sensor which comprises two strip type glucose sensing electrodes the potential differences between which are used to measure blood glucose levels. Of the two glucose sensing electrodes, one has an active surface comprising an organic conducting redox salt dispersed in a polymeric membrane, with the membrane coating a conductive strip while the other is a strip type Ag/AgCl reference electrode having its active surface separated from physical contact with the strip type glucose sensor. Between the two electrodes is filled a carrier strip of water absorbent paper or film which contains an enzyme system and an oxidizable dye. This sensor is capable of measuring a relatively low concentration of glucose and keeping constant the potential differences according to glucose levels, thereby detecting glucose levels with high accuracy. However, a significant disadvantage is an economical unfavorableness because the electrodes, relatively expensive, must be discarded after they are used once.
U.S. Pat. Nos. 5,059,394 and 5,179,005 disclose glucose sensing apparatuses having glucose sensing chambers which comprise glucose oxidase, peroxidase and dye capable of reacting with hydroperoxide to cause a color change. When glucose is oxidized by the glucose oxidase, hydroperoxide is formed which reacts with the dye, causing a color change which is used to measure the blood glucose level with the aid of an optical sensor. This technique is disadvantageous in that it has a very large error margin up to about 10% owing to the fact that many reaction steps are required to obtain results for glucose levels.
The above conventional methods are of indirect measurement rather than direct measurement.